buy shit. if you have tons of candy, buy all the wards you don't already have and put them on shuffle. buy sets for heroes you don't already have sets on. even if you don't play them. buy couriers if you are a courier collector (i don't as i only use my fully gemmed up smeevil riding a mammoth courier). maybe buy announcer packs that you don't have. (i do and i put my announcers on shuffle). all you need is 16 candies for one arcana. so if u keep 32 candies for 2 arcanas, you should be free to use most rest of em candies.
every time u buy an item, a new item will replace it. so this could increase your chance at getting an arcana.
ive already suggested this to other people in different "i didn't get arcana" posts. so i figured il'l make a post my self and put it here for all to see : p
Source: https://www.reddit.com/r/DotA2/comments/10486b8/my_suggestion_to_increase_your_chance_at_trying/
